Such a hydraulic control and such a method are known from DE 198 00 721 A1. In the opening direction, the compensation valve is acted upon by a spring and a pressure, which can be supplied via a fixed throttle. The fixed throttle is part of a pressure divider between the outlet of the compensation valve and the low-pressure connection, which here is a tank connection. Thus, the compensation valve ensures a pressure control, in which the motor inlet pressure has a value, which is substantially determined by the position of the control valve.
In the return pipe from the motor to the low-pressure connection, a compensation valve and a load-retaining valve are arranged in series. Via a pilot pipe the load-retaining valve is supplied with the motor inlet pressure in the opening direction and via a further pilot pipe with the pressure at the outlet of the load-retaining valve. Thus, under the influence of a spring, the load-retaining valve adjusts so that it does not open until the pressure difference has overcome the spring force.
When, now, this motor is lowered under a load, a relatively high inlet pressure is required. For example, the control valve slide has to be opened relatively much, and, in dependence of the design, a larger or smaller slide movement is required to control the high pressure. This is energetically unfavourable, as this high pressure merely has to be available for opening the load-retaining valve.
Another possibility of using the compensation valve is shown in DE 102 16 958 B3. Here, the compensation valve is controlled by a pressure difference over the control valve and keeps the pressure difference over the control valve constant. In this manner, a flow control is realised, in which the amount supplied to the consumer depends on the position of the valve element. The more the valve element is displaced, the larger are the inlet flow and the outlet flow.
U.S. Pat. No. 4,981,159 shows a hydraulic control, which can be used with different valve elements as pressure control on the one side and as flow control on the other side. For this purpose, the valve element, which also has the form of a slide, merely has to be replaced. In principle, such a replacement is not difficult. However, it can only be made, when the system is pressureless or, even better, empty. Thus, a change of operation modes still requires certain efforts.